1. Field of the Invention
This invention relates to a recording apparatus, a reproducing apparatus, and a recording/reproducing apparatus using the recording apparatus and the reproducing apparatus. More particularly, this invention relates to a voice recording apparatus, a voice reproducing apparatus, and a voice recording/reproducing apparatus which are suitable for use in a telephone or the like.
2. Description of the Prior Art
FIG. 12 illustrates a prior art voice recording/reproducing apparatus having recording and reproducing systems. The recording system comprises an A/D converter or sampler 122, and an encoder 123. An analog voice signal input through an input terminal 121 is converted into a digital signal by the A/D converter 122. The digital signal output from the A/D converter 122 is encoded by the encoder 123 using the adaptive differential pulse-code modulation (ADPCM) system. The data output from the encoder 123 are stored in a voice recording memory 124 under the control of a central processing unit (CPU) 125. The reproducing system comprises a decoder 126, and a D/A converter 127. The encoded data read out from the voice recording memory 124 under the control of the CPU 125 are supplied to the decoder 126 to be decoded. The output of the decoder 126 is converted into an analog signal by the D/A converter 127, and then output through an output terminal 128.
In the voice recording/reproducing apparatus utilizing a digital signal processing technique shown in FIG. 12, the data compression rate depends upon the sampling rate of the A/D converter 122 and the type of the encoding system used in the encoder 123. When memories of the same capacity are used, the period of time useful for recording becomes longer with the increase of the data compression rate. In other words, a smaller memory capacity is required to record a voice data set corresponding to a constant period of time.
A small-sized apparatus such as a telephone is allowed to mount a voice recording memory having a small capacity due to the reduced manufacturing cost and the limited volume of the apparatus. This requires a recording/reproducing apparatus to perform the data processing with a high data compression rate. Conventionally, in order to increase the data compression rate in a recording/reproducing apparatus, such countermeasures are performed that the sampling rate is lowered, or that a high rate encoding system is used.
If the sampling rate is lowered, however, the high frequency region of a voice signal is cut, so that there arises a problem in that the quality of voice, especially of a woman's voice, is extremely deteriorated. When a high rate encoding system is used, there exists a problem in that the tone quality is lowered in relatively simple encoding systems such as an ADPCM system. Although it is possible to use another encoding system in which a high encoding rate can be used without reducing the tone quality, there arises problems in that such an encoding system is complicated and that an encoding device using such an encoding system has a complex structure and is expensive.